Abstract
In this study, we conducted numerical simulations of steam injection into a
horizontal well. A sandy-shale layer with thickness of 1 metre is located 2
metre above a horizontal injection well. The numerical simulations intend to
study the variations of the stress state and the permeability in the
sandy-shale layer during steam injection, and to provide useful effective
stress paths for laboratory experiments to follow when testing material
properties of the sandy-shale. A self-developed coupled geomechanics and
thermal multi-phase flow simulator was employed to conduct the simulation
cases. A strain-induced permeability model was used to describe the anisotropic
permeability change of the sandy-shale caused by steam injection. The
simulation results demonstrate that the permeability of 5 and 50 md for the
sandy-shale in two simulation cases is sufficient to allow pore pressure
dissipation to occur, therefore, preventing tensile or shear failure of
sandy-shale as a result of high thermal-induced pore pressure. The stress paths
within the sandy-shale are approaching the failure envelope as steam injection
goes on indicating simultaneous influence of the temperature and the pore
pressure on the stress state change.
Introduction
Sandy-shale formations of several metres in thickness frequently exist in
oil sands deposit. Their material properties, sedimentary characteristics and
distribution in a steam-assisted gravity drainage (SAGD) reservoir are
important factors that determine SAGD performance and strategies of positioning
horizontal well-pairs. It has been confirmed that sandy-shale formations are
usually very sandy and discontinuous; therefore, they are expected to be
permeable to varying degrees during SAGD operations. This is completely
different from the interbedded shales that have extremely low permeability and
can be considered as impermeable.
Analysis of stress state change and anisotropic permeability variation in
the sandy-shale requires conducting coupled simulation of geomechanics and
thermal reservoir flow. Numerical modelling of the coupled processes is
historically carried out in the areas of geomechanics modelling and the
reservoir simulation. Gutierrez and Lewis(1) extend Biot’s theory to
multi-phase fluid flow in deformable porous media. Based on their formulation,
they conclude that the coupling between the geomechanics and the multi-phase
flow occurs simultaneously. Thus, fully coupled system equations of
deformations, multi-phase flow and heat transfer should be solved
simultaneously.
© 2010. Society of Petroleum Engineers
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History
- Original manuscript received:
26 March 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
23 November 2009
- Manuscript approved:
4 December 2009
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